1. Field of the Invention
This invention relates to a method and system for measuring the density of liquids.
2. Description of the Prior art
There have been previously proposed liquid density measurement systems which are based on the theoretically predictable variation of dielectric constant of a non-polar liquid with changes in density of the liquid. Such a system may incorporate a capacitance probe to measure the dielectric constant of the liquid that occupies the space between plates of the probe. An a.c. signal is generated, the magnitude of which is proportional to the probe capacitance and thus to the value of the dielectric constant of the liquid. This a.c. signal is then processed in suitable circuitry to give an output signal representative of the liquid density for feeding, for example, to a digital display unit.
A drawback of such a system is that changes in the composition of the liquid under measurement gives rise to errors in the indicated density since, in general, the relationship between the liquid dielectric constant and liquid density will vary with liquid composition. Where the liquid under measurement is, for example, liquid natural gas (LNG) this drawback can be considerable since the composition of L.N.G. is variable over a wide range and may change due to boil off of certain fractions.